The invention relates to a device and a process for evaporating at least one substance.
Devices referred to as rotary evaporators are known, for evaporating substances, particularly for evaporating solvents when concentrating or distilling pharmaceutical or chemical products. With these rotary evaporators, the liquid substances to be evaporated are placed into the cavity of a rotating flask (evaporation vessel) generally rotatable in a heating bath. By rotating the flask, a thin liquid film is generated on the inside of the rotating flask, from which the substances, particularly the solvent, evaporate. A certain portion of the substance or the solvent also evaporates directly from the surface of the liquid in the rotating flask. The vapor is conveyed from the rotating flask via a vapor line to a condenser where it condenses out again. In general, a negative pressure or vacuum is also generated in the rotating flask in order to increase the vapor pressure of the substances to be evaporated and to protect the product. The vapor line is connected in a passage area to the rotating flask via a rotatable connection. The connection point is sealed by means of a rotary gasket.
Patent specification DE-PS 1 224 062 discloses a rotary evaporator with a work flask that can be rotated around its axis of symmetry via a motorized drive. The work flask can also pivot freely around a swiveling axis running perpendicular to its axis of symmetry, whereby it floats freely on the surface of a water bath. In a rotary evaporator with such a pendulum system, the force of the weight of the work flask with the substance contained therein and to be evaporated is held in the water bath solely by the buoyancy of the work flask and in this way, torques and forces on the mounting of the work flask are clearly reduced.
A process for vacuum rotary evaporation as well as a device for carrying out the process is known from DE 35 11 981 C2. This known rotary evaporator has a pendulum system in which the rotating flask is held floating with free buoyancy on or in a liquid bath. The vertical position of the rotating flask relative to the surface of the liquid of the liquid bath is measured directly or indirectly and used as the regulating value of a regulating path or as control value of a control path to regulate or control the filling content of the rotating flask. The vertical position of the rotating flask relative to the surface of the liquid represents a direct measure for the filling content of the rotating flask, that is, the quantity of liquid that is in the rotating flask. As setting value to regulate this vertical position and thus the filling content of the rotating flask, the directly fed liquid to be evaporated is used. A corresponding setting element (magnet valve) makes it possible to feed liquid to be evaporated in rotating flasks and blocks them in order to keep at the desired setting value the filling content of the rotating flask with the liquid to be evaporated. In this way, there is always enough medium to be processed in the rotating flask that its inner surface is predominantly wetted with the medium during the rotation. The rotary evaporator thereby works with a good efficiency. To detect the vertical position of the rotating flask relative to surface of the liquid, the change in its angle position relative to a stationary mounting, e.g. a stand, can be measured with an inclinometer containing a rotary potentiometer, or a resistance that is perpendicular to the surface of the liquid and changes with the vertical position.
Another rotary evaporation process and another rotary evaporator are known from DE 35 22 607 A1 in which the mass content of the rotating flask or a change in this mass content corresponding to the rotating flask penetrating into bath liquid is ascertained by weighing and the result of the weighing is then used as regulating value or control value for the evaporation process. The rotating flask is held floating with buoyancy on or in a liquid bath, particularly by a pendulum system or a linear lift and lowering system. The weighing of the mass content of the rotating flask can be determined indirectly by weighing the bath with the liquid or weighing the rotating flask with drive system and stand or condenser or by weighing the flask mass content and the distillate mass or by weighing the product before it is inserted into rotating flask or measuring the volume of the rotating flask, or also weighing the quantity of distillate during or after the distillation or ascertainment of its volume. Since the power consumption of the driving torque of the drive also changes when the flask mass content changes, the power consumption or the driving torque or braking torque of the drive of the rotating flask system can also be directly or indirectly measured and used as a regulating value or control value of the evaporate process. In another variant of this known rotary evaporator, the buoyancy on the rotating flask in the bath can be measured and used as a regulating value or control value. The buoyancy can be measured particularly by force, tension, pressure or torsion measuring elements, particularly extensometers, to ascertain the buoyancy force. The buoyancy is also a direct measure for the flask mass content. As regulation for the evaporation process, only the product supply is mentioned in DE 35 22 607 A1, with a reference to the older DE 35 11 981 C2. The mass of the total content of the rotating flask is thus regulated or controlled. Further regulations or controls besides that of the level of filling of the rotating flask are not indicated.
Another form of construction of a rotary evaporator is known from DE 33 30 764 A1 in which the rotating speed of the rotating flask is scanned and the rotating speed is slowed in time-controlled manner within a predetermined interval from a predetermined starting speed to a lower final speed.
Another rotary evaporator is known from CH 411 783 in which the rotating speed of the rotating flask can be modified. CH 411 783 does not mention the conditions based on which the rotating speed is changed.
Another publication, DE 199 09 228 A1, then discloses a process and a device for condensing liquid samples to a specific residual volume with a rotating evaporation flask designed bulb-shaped with a bulging upper area and a tapering extension in the lower area. This evaporation system differs from the previously described rotary evaporators firstly in that the axis of rotation of the evaporation flask is oriented vertically, that is parallel to the force of gravity. In this way, the liquid medium gathers in the lower, tapered area of the evaporation flask as long as the flask does not rotate. For an evaporation process, however, the evaporation flask is then rotated quickly enough that the entire medium rises upward into the bulging area due to centrifugal forces and a thick film forms there on the inner wall. The rising of the medium into the bulging area is controlled with a light barrier arranged at the transition between the bulging area and the extension, to detect the surface of the liquid. During the evaporation process, there is no medium in the lower area or extension of the flask. In addition, the film in the bulging area of the flask is not constantly renewed or redrawn during the evaporation process as is the case in a typical rotary evaporator, rather it remains on the inner wall of the flask until only the residual film is left. For this reason, the efficiency or the evaporation capacity of this rotary evaporator is limited.